thread fit

[Jerry V Lape]

Getting ready to finish up a flintlock and put in the touch hole liner (Chambers).  In the past I have followed the instructions which Chambers provides along with his installation kit and that has worked just fine.  But I started looking at charts for fitment of bolts and became curious about how to select proper fitment taps to insure best strength.  Hoping one of the real machinists on here can shed some light on this subject.  

[Bob Roller]

Getting ready to finish up a flintlock and put in the touch hole liner (Chambers).  In the past I have followed the instructions which Chambers provides along with his installation kit and that has worked just fine.  But I started looking at charts for fitment of bolts and became curious about how to select proper fitment taps to insure best strength.  Hoping one of the real machinists on here can shed some light on this subject.  

Jerry,
Jim Chambers should be able to tell you instantly what drill to use. Is it an odd thread or?

Bob Roller

[Jerry V Lape]

Bob,  I am not questioning Mr. Chambers instructions or the tap he sent to accompany the liner.  The question is more one of education.  For example I read there are three categories of fitment for bolts but couldn't find any instruction on how they are created or measured.  I would be happy to be directed to other sites to learn more about this topic.  Is the fit a function of just the tap drill size or are there more than one tap for each particular size bolt?  I  don't even know enough to ask the question correctly.

[Bob Roller]

Bob,  I am not questioning Mr. Chambers instructions or the tap he sent to accompany the liner.  The question is more one of education.  For example I read there are three categories of fitment for bolts but couldn't find any instruction on how they are created or measured.  I would be happy to be directed to other sites to learn more about this topic.  Is the fit a function of just the tap drill size or are there more than one tap for each particular size bolt?  I  don't even know enough to ask the question correctly.

Jerry,
At one time there were standards set by the U.S.Bureau of Standards for drill/tap sizes. I think the current thread charts are for about 80% of full depth but am not sure about that either. Today sizes may vary a lot depending on origin of the taps.  Sizes of bolts are also questionable depending on origin.It's been over 50 years since I delved into this subject because of constant use of the same sizes over and over for decades.
In 1971 I took a job in a production shop that catered to the coal mining industry and was told we don't cut class 3A threads which was I think a precise thread that took a lot of time.MOST of what we did was done on a Colter Thread Mill. On occasion I did an Acme thread but remember little about it.
Maybe someone more up to date than me can set both of us straight.

Bob Roller

[Bob Roller]

Getting ready to finish up a flintlock and put in the touch hole liner (Chambers).  In the past I have followed the instructions which Chambers provides along with his installation kit and that has worked just fine.  But I started looking at charts for fitment of bolts and became curious about how to select proper fitment taps to insure best strength.  Hoping one of the real machinists on here can shed some light on this subject.  

Jerry,
Jim Chambers should be able to tell you instantly what drill to use. Is it an odd thread or?

Bob Roller

Jerry,
Type in U.S.Bureau of Standards for screw threads and all sorts of things will pop up regarding this subject.

Bob Roller

[davec2]

Get yourself a copy of the Machinery Handbook......

http://www.amazon.com/s/?ie=UTF8&keywords=machinery%27s+handbook&tag=googhydr-20&index=aps&hvadid=49832368945&hvpos=1t1&hvexid=&hvnetw=g&hvrand=8872281027401553391&hvpone=&hvptwo=&hvqmt=b&hvdev=c&ref=pd_sl_9bh0gjicgc_b

Simple tutorial....

http://www.fastenal.com/content/feds/pdf/Article%20-%20Screw%20Threads%20Design.pdf

[Acer Saccharum]

Above all, use a drill press for installing liners.

The liner calls for a certain tap drill, but DON'T just use this drill. It will drill oversized.

Start with a center punch, a combined drill and countersink, then a pilot hole, then a size smaller than the tap drill. This leaves a very small amount for the tap drill to cut, and will give you a better size.

I put the tap in the drill chuck, bring it down to contact the work, then I turn the chuck by hand as far as I can. This starts the tap nice and straight. Finish with a tap wrench.

[chubby]

I agree with Acer a letter or number drill 5to 8 thou. under is good it will cut a little bigger! it works better for a fine thrd. tap like the 32tpi. for the white lightning liner. you will get a great fit! and remember be sure the drill will not hit the plug face or it will push off cutting bigger and ruin the hole. Chubby

[Bob Roller]

Above all, use a drill press for installing liners.

The liner calls for a certain tap drill, but DON'T just use this drill. It will drill oversized.

Start with a center punch, a combined drill and countersink, then a pilot hole, then a size smaller than the tap drill. This leaves a very small amount for the tap drill to cut, and will give you a better size.

I put the tap in the drill chuck, bring it down to contact the work, then I turn the chuck by hand as far as I can. This starts the tap nice and straight. Finish with a tap wrench.

This is solid advice and all of the (few)liners I have installed were done using this method. One added thing,
countersink the finished hole the depth of ONE full thread and it will let the tap start easily and no upheaval
around the tapped hole.

Bob Roller

 

[P.W.Berkuta]

Davec2 & Acer's answer are correct along with Chubby -- get the handbook - also you don't need the latest version either. Go to Amazon or Ebay and buy a older used book it still has the same info on threading.

[Steve-In]

I agree with the Handbook.  You do not need the latest version my 14th is not much different than my 25th. 
Also the class of thread has nothing to do with the size of the hole.  It is determined when it is made.  The most common that I have seen in machine work is 2B.  I am not saying an oversize hole will work.  The liners should be produced and gaged by a specific thread class.  A tap of corresponding class is required to have good fit.

A short tutorial
http://www.accuratescrew.com/TechTips/?TipNO=5

Unfortunatly there are no standards that I am aware of for proper thread classes for barrels, breechplugs, liners, nipples or drums.

[Steve-In]

A good link to taps and what the "H" number means.

http://tapmatic.com/tapping-questions/class-of-threads-h-limits

[ShutEyeHunter]

Some sage told me years ago to start critical holes with a center drill like you use on a lathe. They are very stiff with short flutes that wont wander away from the center punch. I saw them in ML builders supply catalog if you cant find one locally

[P.W.Berkuta]

Some sage told me years ago to start critical holes with a center drill like you use on a lathe. They are very stiff with short flutes that wont wander away from the center punch. I saw them in ML builders supply catalog if you cant find one locally

Quite correct Shut Eye but that only gives a good center for your drill so it don't wonder. After spotting the center mark with the center drill use a 0.010" smaller drill to make a pilot hole then use the correct tap drill to finish the hole - then tap - perferably with the tap in a drill press. If you don't have a drill press use a combination square to keep the tap perpendicular to the work surface.

[Dphariss]

The thread used on Chambers liners is such that finding a tap of a tighter tolerance is difficult to impossible, I tried.
As a result I ended up making my own liner to get a fit I liked.
Dan

[Dphariss]

Some sage told me years ago to start critical holes with a center drill like you use on a lathe. They are very stiff with short flutes that wont wander away from the center punch. I saw them in ML builders supply catalog if you cant find one locally

A center drill requires no punch mark. In fact it can be used to move a punch mark slightly.

Dan

[Steve-In]

Spotting drills are a better choice for good location of holes.  Center drills are for putting a hole in lathe stock to accept a lathe center.  The point is too thick and they are weak in that area.  Spotting drills are designed to precisely place a start for a drill.  They are stronger and if you do manage to break one it is easier to get the chips out.
https://www.mscdirect.com/browse/tn/Holemaking/Center-Drills-Combination-Drill-Countersinks-Spotting-Drills/Spotting-Drills?navid=12106130

Most people do not understand that the point of a drill does not cut.  It pushes material around and generates heat through the cut.

 Dphariss  Where I used to work we produced a lot of fine pitch threads in aluminum and steel.  Our preferred method was to spot drill/chamfer, drill, ream ( to hold minor diameter closer ) and thread mill.  Almost no scrap this way.  Very few home shops can thread mill though.

[Daryl]

I measured some barrel breech threads on an Indian made Brown Bess (came without a vent) that were .085" deep - Very coarse.  The threads of the breech plug from that gun engaged the barrel threads .057", .022" and .002" - good fit? Yeah - only 3 engaged.  The breech plug's threads were a BIT tapered and appeared to have been cut, for the most part, (or maybe only chased) with a file.
I sent the gun back for a refund which was returned, but the company wrote me claiming my concerns were unfounded as their local "gun smith" had proofed the musket and it was just fine. I took the money returned and ran.

[FL-Flintlock]

their local "gun smith" had proofed the musket and it was just fine.

It didn't blow-up 'this time' so it must be good.

SMH that people still think that is acceptable testing. 

[Turtle]

 I tried a smaller tap drill also-no go.I set up the drill press with enough travel so I can change drill bits and install the countersink and tap all while left in position in the drill press. I use blue locktite on the liner for sealing and anti-seize. After finished, I pull the breach plug and dremel off any liner intruding in the barrel.
                                                            Turtle

[Scota4570]

"Fitment"  Noun,  a piece of furniture or equipment made especially for a particular room or space.

Fitment  does not mean the precession of how things fit together.  I see "Fitment"  being used more and more to describe fit and finish of gun parts.  Also, it is being used regarding automobile tires.  I guess the language is changing. 

[ShutEyeHunter]

Spotting drills are a better choice for good location of holes.  Center drills are for putting a hole in lathe stock to accept a lathe center.  The point is too thick and they are weak in that area.  Spotting drills are designed to precisely place a start for a drill.  They are stronger and if you do manage to break one it is easier to get the chips out.
https://www.mscdirect.com/browse/tn/Holemaking/Center-Drills-Combination-Drill-Countersinks-Spotting-Drills/Spotting-Drills?navid=12106130

Thanks Steve for the better mousetrap. I always learn something from this forum.  Everything I know about metalworking is from doing it at least twice and messing it up.